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Abstract:

A method for removing contaminants such as oil and solids from water by
feeding a mixture of water containing the contaminants and carbon dioxide
to a cyclone; separating water from the mixture; separating a second
mixture of oil, carbon dioxide and water from the mixture and feeding the
second mixture to a separator wherein oil, carbon dioxide and water are
recovered from the separator.

Claims:

1. A method for removing contaminants from water comprising the steps: a)
feeding flocculent solution to water containing contaminants, wherein the
flocculent disperses in the water; b) feeding carbon dioxide to water
containing contaminants, wherein the carbon dioxide dissolves in said
water; c) feeding the water containing the dissolved carbon dioxide to a
cyclone separator; d) recovering water from said cyclone separator; and
e) recovering oil from said cyclone separator.

2. The method as claimed in claim 1 wherein said water is selected from
the group consisting of produced water and process water in refineries
and petrochemical plants.

3. The method as claimed in claim 1 wherein said contaminants are
selected from the group consisting of oil and solids.

4. The method as claimed in claim 1 wherein said flocculent solution is
prepared from flocculent that is effective at acidic pH ranges from 3.0
to 6.5 in aqueous phase.

5. The method as claimed in claim 1 comprising controlling pressure of
the water containing the dissolved carbon dioxide prior to entry into the
cyclone separator.

7. The method as claimed in claim 1 further comprising recovering said
carbon dioxide from said oil.

8. The method as claimed in claim 1 wherein said recovered carbon dioxide
is fed to water containing contaminants.

9. The method as claimed in claim 1 wherein bubbles are formed in said
water containing dissolved carbon dioxide by the pressure control.

10. The method as claimed in claim 9 wherein bubbles are formed in said
mixture being introduced into said cyclone separator.

11. The method as claimed in claim 1 wherein said oil is selected from
the group consisting of dissolved oil and emulsified oil.

12. The method as claimed in claim 1 wherein said water containing carbon
dioxide is mixed in a gas dissolving device.

13. The method as claimed in claim 1 further recovering carbon dioxide.

14. The method as claimed in claim 13 wherein said recovered carbon
dioxide is fed to said device.

15. The method as claimed in claim 1 wherein the pH of said water
containing carbon dioxide ranges from 4 to 7.5.

16. A method for removing contaminants from water comprising feeding a
mixture of water containing contaminants and carbon dioxide to a cyclone;
separating water from said mixture; separating a second mixture of oil,
carbon dioxide and water from said mixture and feeding said second
mixture to a separator wherein oil, carbon dioxide and water are
recovered from said separator.

17. The method as claimed in claim 16 wherein said contaminants are
selected from the group consisting of oil and solids.

18. The method as claimed in claim 16 wherein said water is selected from
the group consisting of produced water and process water in refineries
and petrochemical plants.

19. The method as claimed in claim 16 wherein said mixture is present in
a tube having a length from 0.5 to 100 meters.

20. The method as claimed in claim 16 wherein pressure of said mixture is
controlled prior to entry into said cyclone.

21. The method as claimed in claim 16 wherein said water recovered from
said second mixture is fed to join said water separated from said
mixture.

22. The method as claimed in claim 21 wherein bubbles are formed in said
mixture being introduced into said cyclone.

23. The method as claimed in claim 17 wherein said oil is selected from
the group consisting of dissolved oil and emulsified oil.

24. The method as claimed in claim 17 wherein said mixture is mixed in a
gas dissolving device.

25. The method as claimed in claim 24 wherein said recovered carbon
dioxide is fed to said device.

26. The method as claimed in claim 16 wherein the pH of said mixture
ranges from 4 to 7.5.

27. A method for removing contaminants from water comprising the steps:
a) feeding a mixture of water containing oil, solids, flocculent, and
carbon dioxide to a cyclone; b) separating water from said mixture; c)
separating a second mixture of oil, carbon dioxide and water from said
mixture; d) feeding said second mixture to a separator; and e) recovering
said oil.

28. The method as claimed in claim 27 wherein said water is selected from
the group consisting of produced water and process water in refineries
and petrochemical plants.

29. The method as claimed in claim 27 wherein said mixture is present in
a tube having a length from 0.5 to 100 meters.

30. The method as claimed in claim 27 wherein pressure of said mixture is
controlled prior to entry into said cyclone.

31. The method as claimed in claim 27 wherein said water recovered from
said second mixture is fed to join said water separated from said
mixture.

32. The method as claimed in claim 31 wherein bubbles are formed in said
mixture prior to introduction into said cyclone.

33. The method as claimed in claim 27 wherein said oil is selected from
the group consisting of dissolved oil and emulsified oil.

34. The method as claimed in claim 27 wherein said flocculent works at
acidic pH ranges from 3.0 to 6.5 in aqueous phase.

35. The method as claimed in claim 27 wherein said mixture is prepared by
dissolving carbon dioxide in said water in a gas dissolving device.

36. The method as claimed in claim 35 wherein said gas dissolving device
is a venturi device.

37. The method as claimed in claim 35 wherein said recovered carbon
dioxide is fed to said device.

38. The method as claimed in claim 27 wherein the pH of said mixture
ranges from 4 to 7.5.

Description:

BACKGROUND OF THE INVENTION

[0001] The invention relates to a process in which flotation of dispersed
oil in water is accelerated in a hydrocyclone separator by carbon dioxide
bubbles that are generated from dissolved carbon dioxide in the
oil-bearing water after a pressure drop.

[0002] Produced water is the water that is produced with crude oil brought
to the surface. On average, more than ten barrels of produced water is
generated for each barrel of oil. Produced water normally contains high
concentration of super fine oil droplets in the form of emulsions
stabilized by surfactants or other emulsifying agents. It is well known
that it is difficult to remove oily contaminants from wastewater and
other natural and industrial wasters containing oil since
de-emulsification and oil extraction from such contaminated water can be
particularly challenging. Removal of the emulsified oil in water requires
the addition of emulsion breaking reagents such as flocculants.
Acidification using an inorganic acid or carbon dioxide to facilitate
precipitation of emulsified oil is another effective emulsion breaking
process.

[0003] Hydrocyclones can be used to separate liquids and solids or liquids
of different densities. Because hydrocyclones do not require any pre- or
post-treatment of the produced water or any addition of chemicals, they
have been used extensively for produced water treatment. Some
hydrocyclones can even remove particles in the range of 5 to 15 microns,
but hydrocyclones cannot remove dissolved oil and grease components.
Flotation is another widely employed method to treat produced water or
other oily water. Through the aggregation and flotation effect of fine
gas bubbles, flotation can remove small and suspended particles that are
difficult to separate by settling or sedimentation. Coagulation reagent
can be used as a pretreatment to flotation. Gas flotation technology can
be classified into two categories by the method used to generate gas
bubbles and the resultant bubble sizes: dissolved gas flotation or DGF
and induced gas flotation or IGF. In a DGF process, gas is dissolved in
water under elevated pressure and released into a flotation chamber. Upon
release, larger amounts of fine gas bubbles 20 to 100 microns in diameter
are generated due to rapid pressure drop. The dissolved gas can be air,
nitrogen or another type of inert gas such as methane. Dissolved gas
flotation can also be used to remove volatile organics and oil and grease
if the gas to water volume ratio is high enough. Compared to DGF
technology, IGF technology uses mechanical shear or propellers to create
bubbles that are introduced into the bottom of the flotation chamber.

[0004] The efficiency of the flotation process is affected by the
differences in density of liquid and the contaminants to be removed, and
the dispersion situation of contaminants such as oil droplet size and
temperature. Normally, a low temperature is preferred due to high
solubility of gas in the liquid phase and high surface tension of the
liquid phase. Also, the gas bubble size and size distribution are
critical to the removal efficiency. Removal of particles as small as 3 to
5 microns in size can be achieved by dissolved air flotation or DAF if a
coagulation reagent is added for pre-treatment. Further, the total
removal of oil can be higher than 93%.

[0005] Flotation, however, is not the most effective technology for the
removal of dissolved oil from water because the volume ratio of gas to
water is mostly lower than 0.15:1 in DAF systems and it is difficult to
achieve higher ratios. Another drawback is that the gas-supersaturated
water which is forced through needle valves or special orifices to
generate bubbles must be fresh water or cleaned water to avoid clogging
of such orifices with particles carried in the water. This can increase
operating cost of DAF by lowering throughput capacity.

[0006] A combined cyclone separation and gas flotation technology called
air-sparged hydrocyclone or ASH has circumvented some of these
disadvantages of gas flotation technologies. In the air-sparged
hydrocyclone, gas is pumped through a porous cylindrical membrane that is
coupled to the liquid-liquid hydrocyclone while wastewater is pumped
through the hydrocyclone. Because the bubbles are sheared off the wall of
the porous membrane due to large centrifugal forces inside the
hydrocyclone, much smaller gas bubbles are generated compared to those in
DAF. Also the gas flotation effect is not dependent on the gas
solubility, so the air to water ratios can be as high as 100:1 to achieve
partial removal of the dissolved oil. A concern with ASH is that the low
froth concentration in the overflow duo to maintenance of large
volumetric overflow rate requires additional treatment steps and the
operational parameters of an ASH device are limited by the requirement of
obtaining a steady overflow.

[0007] To address the operational limitations caused by the traditional
stream-splitting approach of hydrocyclones, U.S. Pat. No. 6,171,488
discloses a bubble accelerated flotation technology or BAF evolved from
ASH technology. The BAF device consists of a bubble chamber (BC) and a
BAF tank. In the BAF process, although coagulation and flocculation of
contaminants are completed in the bubble chamber, the generated froth is
not ejected through an overflow device. The separation of water and froth
is finished in the BAF tank connected to the bubble chamber. Because the
BAF process does not incorporate a cleaned-water underflow restriction,
operation of the hydrocyclone is more stable. A drawback of the BAF
technology is that it requires an additional large flotation tank to
separate the aggregated contaminants since the effluent flow is not
divided in the hydrocyclone. The treating capacity is determined by the
volume of the BAF tank. Another drawback is that this technology has not
avoided the fouling problem of the porous membrane. Induced air bubble
chamber, vacuum flotation bubble chamber and electro-flotation bubble
chamber have been derived from this technology to address this fouling
problem. In-situ addition of a coagulant and flocculent can also improve
oil removal efficiency.

[0008] U.S. Pat. No. 7,638,062 teaches another cyclonic gas flotation
process that adds non-soluble gas such as natural gas into produced water
before water is tangentially injected into a cyclonic device. The gas
bubbles are generated in the water pipeline through a gas disperser to
create micro bubbles in the aqueous phase. One drawback of this
technology is that the gas bubbles are dispersed in water through
mechanical measures rather than through altering the solubility of the
gas in the aqueous phase so the gas bubbles are not homogenously
generated and small enough to achieve total removal of the emulsified
oil. Another drawback is that the volume ratio of gas to water cannot be
as high as the ratio in an air-sparged hydrocyclone which is essential
for removal of dissolved oil in water.

[0009] The relative disadvantages of the above processes can be addressed
by the methods of the invention. Carbon dioxide can be dissolved in oil
water prior to it entering a cyclone separator. Dissolving carbon dioxide
in water provides several advantageous properties to the overall process.
Carbon dioxide can partially de-emulsify oily water and reduce the
solubility of organics in water by its acidifying effect. Also, after
pre-treatment of oily water, carbon dioxide does not require the
generation of large amounts of fine bubbles in the cyclone to achieve
satisfactory removal efficiency of emulsified oil and dissolved oil.
Furthermore, the volume ratio of carbon dioxide to water can be precisely
controlled to avoid unstable operation of the cyclone and keep a minimal
overflow rate. Because of carbon dioxide's high solubility in water and
the relatively simpler structure of the conventional hydrocyclone, the
operating cost and construction cost can be greatly reduced. Another
advantage of adding carbon dioxide is that it can treat warm and hot
produced water. This can be important for the fast treatment of water in
some oil fields where the produced water's temperature is higher than the
ambient temperature. Since the solubility of carbon dioxide in water is
much higher than that of air, direct treatment of warm and hot produced
water is possible.

[0010] Because some produced water contains high concentrations of
chemical additives and metal cations that stabilize emulsion, dissolving
carbon dioxide in the water may not achieve the desired coagulation
effect. Addition of auxiliary flocculent which works at acidic pH ranges
from 3.0 to 6.5 in water may be needed to accelerate coagulation of the
emulsified contaminants. Addition of the flocculent is optional and is
determined by the treatment requirement. The flocculent is selected from
the group consisting of organics such as modified polyacryamides and
bioflocculents; inorganics such as ferric sulfate and aluminum sulfate;
or combinations of both. Flocculent can be added before or after
dissolving of carbon dioxide in the water.

SUMMARY OF THE INVENTION

[0011] A method for removing contaminants from water comprising the steps
is disclosed:

[0013] b) feeding flocculent solution to water containing contaminants and
carbon dioxide, wherein the flocculent disperses in the water;

[0014] c) feeding the water containing the dissolved carbon dioxide to a
cyclone separator;

[0015] d) recovering water from the cyclone separator; and

[0016] e) recovering oil from the cyclone separator.

[0017] The water is typically produced water or industrial process water
and the contaminants are selected from the group consisting of oil and
solids. The oil may be dissolved oil or emulsified oil.

[0018] The water containing carbon dioxide is typically prepared by
dissolving carbon dioxide in the water through a venturi device or a
mixing valve. The recovered carbon dioxide may be returned to this device
for use in introducing carbon dioxide into the water. The resulting
mixture typically has a pH of 4 to 7.5.

[0019] The flocculent solution is prepared from flocculent that works at
acidic pH ranges from 3.0 to 6.5, and is selected from the group
consisting of modified polyacryamides, bioflocculents, ferric sulfate,
aluminum sulfate, or any combination of them. The optimum effective
flocculent dose depends on the contaminants concentration and the nature
of contaminants in water.

[0020] The method controls the pressure of the water containing the
dissolved carbon dioxide prior to entry into the cyclone separator.

[0021] The carbon dioxide in the overflow is recovered and is fed to the
water containing contaminants through the gas dissolving device.

[0022] In another embodiment of the invention there is disclosed a method
for removing contaminants from water comprising feeding a mixture of
water containing contaminants and carbon dioxide to a cyclone; separating
water from the mixture; separating a second mixture of oil, carbon
dioxide and water from the mixture and feeding the second mixture to a
separator wherein oil, carbon dioxide and water are recovered from the
separator.

[0023] The contaminants are selected from the group consisting of oil and
solids and the water is produced water or process water in refineries and
petrochemical plants. The oil may be dissolved oil or emulsified oil. The
mixture is present in a tube or line having a length from 0.5 to 100
meters and the pressure of this mixture is controlled prior to entry into
the cyclone. The mixture is prepared by inputting the carbon dioxide and
any recycled carbon dioxide in water through a device such as a venturi
or a mixing valve. The pH of the mixture ranges from 4 to 7.5

[0024] In a different embodiment of the invention, there is disclosed a
method for removing contaminants from water comprising the steps:

[0025] a) feeding a mixture of water containing oil, solids and carbon
dioxide to a cyclone;

[0026] b) separating water from the mixture;

[0027] c) separating a second mixture of oil, carbon dioxide and water
from the mixture;

[0028] d) feeding the second mixture to a separator; and

[0029] e) recovering the oil.

[0030] The water may be produced water. The oil may be dissolved oil or
emulsified oil. The mixture is present in a tube or line having a length
from 0.5 to 100 meters and the pressure of this mixture is controlled
prior to entry into the cyclone. The mixture is mixed in a device such as
a venturi for inputting the water, the carbon dioxide and any recycled
carbon dioxide. The pH of the mixture ranges from 4 to 7.5

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The FIGURE is a schematic for removing contaminants in water per
the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0032] Turning to the FIGURE, a carbon dioxide accelerated
de-emulsification and cyclonic flotation process is shown. In this
process, carbon dioxide is dissolved in water containing solids and oil,
particularly dissolved oil and emulsified oil, through a gas dissolving
device or a venturi tube.

[0033] Carbon dioxide from a feed source such as a tanker truck or storage
tank is fed through line 1 and through open valve V1 to line 2 where it
enters a gas dissolving device, G. A pH probe, not shown, may be
installed in the pressure pipeline and be used to adjust the pH to a
range of 4 to 7.5, particularly 5 to 6.5 by controlling the rate of
addition of the carbon dioxide. The pressure of the carbon dioxide
pipeline ranges from 100 KPa to 2 MPa, with a range of 150 KPa to 1 MPa
preferred. This pressure can in part be controlled by the carbon dioxide
compressor F discussed below which helps feed recycled carbon dioxide
back to combine with the fresh feed of carbon dioxide. Produced water,
which contains dissolved oil and emulsified oil as well as solids is fed
through line 3 to water pump A which pressurizes and feeds the produced
water through line 4 to gas dissolving device G. Flocculent solution is
fed through valve V2 in the produced water. Addition of flocculent in the
produced water is optional and its dose depends on the contaminants
concentration and the nature of contaminants in water. The carbon dioxide
will dissolve in the produced water in gas dissolving device G and be fed
through line 5 to pressure control valve V3. The length of line or tube 5
can be from 0.5 meters to 100 meters, with a length of 1 meter to 20
meters preferred. This length will allow sufficient residence time for
emulsion breaking and coagulation of oil in the produced water to occur.
The pressure control valve V3 will control the hydraulic pressure of the
acidified water in line 5. Once the acidified water passes through the
pressure control valve V3, micro bubbles can be instantly generated due
to the pressure drop. The produced water with carbon dioxide dissolved
therein continues through line 5 to cyclone B.

[0034] The acidified water will be tangentially introduced into the
cyclone where the oil droplets are collected by bubbles and aggregated in
the center of the cyclone. The water flow rate between the overflow to
the underflow ranges from 0.01:1 to 1:1 with a range from 0.02:1 to 0.2:1
preferred.

[0035] In the cyclone B, the solids and the dissolved and emulsified oils
are separated. The water will be removed from the cyclone B through line
9 and open valve V5 through line 10 to water tank D. Some carbon dioxide
will remain dissolved in the water removed through line 9 as well as
having oil droplets contained therein and is recovered from water tank D
through line 11 where it is fed into carbon dioxide tank E. The carbon
dioxide tank E will feed the recycled carbon dioxide through line 12 to a
compressor F and through open valve V6 where it will enter line 2 and
begin the process anew by entering the gas dissolving device G.

[0036] The separated oil from the cyclone B will, with water (froth) and
dissolved carbon dioxide, is fed through line 6 and open valve V4 to line
7 where it will enter the separation tank C. The separation tank is an
induced gas flotation tank or a gravimetric flotation tank. Separated
water will be removed through line 14 and fed to line 13 where it will be
recovered. This separated water may still have residual carbon dioxide
present in it and will need to be treated prior to storage as it can be
corrosive in such condition. The separated oil will be removed through
line 15 and recovered. The dissolved carbon dioxide is captured and fed
through line 8 to line 11 where it will be fed to the carbon dioxide tank
E and back to the gas dissolving device G as described above.

[0037] While this invention has been described with respect to particular
embodiments thereof, it is apparent that numerous other forms and
modifications of the invention will be obvious to those skilled in the
art. The appending claims in this invention generally should be construed
to cover all such obvious forms and modifications which are within the
true spirit and scope of the present invention.

Patent applications by Guohua Xiu, Shanghai CN

Patent applications by Zhixiong Cha, Scotch Plains, NJ US

Patent applications in class Including chemical addition (with or without bouyancy gas)

Patent applications in all subclasses Including chemical addition (with or without bouyancy gas)